There are many applications where fluid is stored in a tank and drawn from the tank for use either periodically or continuously. In some cases it is desirable to continuously monitor the level of the fluid within the tank, for example in the case of a gas tank, so that the range of the vehicle can be determined at any time. In other situations, most notably in the case of a windshield washer tank, fluid is drawn out infrequently and a simple indication of when the fluid level is low is all that is needed. When a low fluid level is indicated, sufficient fluid remains so as to allow a refilling of the fluid tank without undue inconvenience. In many instances replacement of non-critical fluids is dependent on the owner or service technician periodically checking the level of the fluid. However, with the demise of the full-service gas station and because of the increased reliability and longer times between periodic maintenance such as oil changes, vehicles may go six months to a year without maintenance. The vehicle operators, because of the greater reliability of vehicles, can be less informed about the mechanical systems of their vehicles and thus less likely to make routine maintenance checks. Nevertheless, the availability of windshield wiper fluid can be more than a convenience if it is necessary to enhance or maintain visibility. A low wiper fluid indicator is desirable even on low cost economy vehicles.
Cost and reliability are influenced by simplicity in construction and assembly. What is needed is a fluid level sensor that meets the criteria of simplicity of construction and assembly.